The invention relates to a multiple-transmission-ratio transmission arrangement such as disclosed in commonly assigned, copending application Ser. No. 463,379, of Heinrich Dick, filed Apr. 23, 1974, the entire disclosure of which is incorporated herein by reference. This transmission arrangement includes an electronic control arrangement which automatically triggers a changeover from one transmission ratio to another. With each changeover of transmission ratio, a frictional gear-changing unit (such as a brake or clutch) which was previously activated is deactivated whereas another frictional gear-changing unit which was previously deactivated is now activated. Furthermore, the electronic control arrangement determines the duration of the deliberately introduced, transitional gear-shift overlap action occurring during the changeover from one transmission ratio to another. The gear-shift overlap action can be positive or negative. A positive gear-shift overlap involves transitional overlap in the activation of the two gear-changing units (brakes or clutches) involved in a transmission ratio changeover, whereas a negative gear-shift overlap involves transitional overlap in the deactivation of the two gearchanging units (brakes or clutches) involved in a transmission ratio changeover. For example, if a particular transmission-ratio changeover involves the hydraulic activation of a brake and the hydraulic deactivation of a clutch, a positive gear-shift overlap would involve deactivating the clutch only after the brake is activated, whereas a negative gear-shift overlap would involve activating the brake only after the clutch has been deactivated. With the type of electronic control arrangement in question, the duration of the gear-shift overlap action, whether positive or negative, can be preset very exactly, and if necessary changed after construction or installation.
It is desirable to be able to set the durations of up-shifting and down-shifting gear-shift overlaps to different values. In application Ser. No. 463,379, to achieve this, each frictional gear-changing unit (hydraulic brake or clutch) is provided with its own respective solenoid through which hydraulic fluid is supplied, and each such solenoid valve is provided with an electronic switch device of its own. Furthermore, the two solenoid valves associated with the changeover from one to the next transmission ratio (e.g., the changeover from second gear to third gear, and back from third gear to second gear) are provided with a single electronic timing stage for introducing a time delay for the gear-shift overlap action. This single timing stage is associated with one of the two solenoid valves; i.e., it delays the deenergization of the associated solenoid valve when the energization of the other solenoid valve is being initiated, and it delays the energization of the associates solenoid valve when the deenergization of the other solenoid valve is being initiated. In this way, it is possible to achieve a positive gear-shift overlap action for every up-shifting transmission-ratio changeover and a negative gear-shift overlap action for every down-shifting transmission ratio changeover.